Red Hat: CVE-2024-58084: kernel: firmware: qcom: scm: Fix missing read barrier in qcom_scm_get_tzmem_pool()

In the Linux kernel, the following vulnerability has been resolved:

firmware: qcom: scm: Fix missing read barrier in qcom_scm_get_tzmem_pool()

Commit 2e4955167ec5 ("firmware: qcom: scm: Fix __scm and waitq
completion variable initialization") introduced a write barrier in probe
function to store global '__scm' variable. We all known barriers are
paired (see memory-barriers.txt: "Note that write barriers should
normally be paired with read or address-dependency barriers"), therefore
accessing it from concurrent contexts requires read barrier. Previous
commit added such barrier in qcom_scm_is_available(), so let's use that
directly.

Lack of this read barrier can result in fetching stale '__scm' variable
value, NULL, and dereferencing it.

Note that barrier in qcom_scm_is_available() satisfies here the control
dependency.